Latching mechanism for optical switches

ABSTRACT

This invention relates to a micro-switch assembly involving a novel magnetic latching mechanism. In one aspect of the present invention, it involves a micromachined structure that comprises an outer frame, an inner frame pivotally connected to the outer frame and rotates when an external electromagnetic force is applied, and a means for latching the inner frame at a given angle of inclination relative to the outer frame. One embodiment of the present invention involves the use of a magnetic material, such as Permalloy, and permanent magnets to achieve the latching result. A Permalloy piece is attached to the inner frame of the micro-switch assembly and a magnet layer is attached to the outer frame. The magnetic force attracting the Permalloy piece and the magnet layer allows the latching of the two frames to occur in the absence of the external applied electromagnetic force. The use of this magnetic latching mechanism allows a reduction in the use of electric current to maintain a movable frame in a micromachined structure or a micro-switch assembly in a fixed position. It provides advantages of greater mechanical and optical stability and less energy consumption. In other embodiments, additional Permalloy pieces can be added to the outer frame to increase the magnetic field, so as to further reduce the electric current necessary for latching and unlatching the frames.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a micromachined structure and toan opto-mechanical switch (micro-switch) incorporating the micromachinedstructure. Specifically, it relates to a latching mechanism incorporatedin the opto-mechanical micromachined switch.

[0003] 2. Description of Related Art

[0004] Micromachines are small electromechanical devices that arefabricated on wafers of silicon and other materials using semiconductormanufacturing techniques. Optical switches in micro-electromechanicalsystems (MEMS) employ tiny mirrors that are etched onto silicon wafers.Such optical switches are commonly used in fiber-optic networks, throughwhich light signals/data are routed. The tiny mirrors can be positionedto intercept the incoming light signals conveyed via the individualstrands of optical fiber. Or alternatively, the mirrors can be pivotedto direct the incoming light beam at a desired angle into a receivingfiber.

[0005] Opto-mechanical switches typically include a light source, alight receiver, and a movable light blocking/reflecting mechanism. Thelight blocking/reflecting mechanism typically includes a drive motorthat is selectively actuated to move a blocking/reflecting member (e.g.,a mirror) between or among different positions, thereby performing themicro-switch function.

[0006] Typically, an electromagnetic drive motor is used to turn on/offthe micro-switch by moving the mirror. In the past, to maintain theswitch in the “on” position, current must be applied continuously tomaintain the electromagnetic force on the mirror. The continuouslyapplied current inherently generates excess heat, which is dissipated tothe neighboring structure, which is undesirable for amicro-electromechanical system. Among other things, this heat can causethe reflective surface and supporting structure to change shape andsize, thereby increasing mechanical and optical instability. Besides,continuous application of electric current also results in high-energyconsumption. This heating problem is exacerbated when a large number ofmicro-switches are used in a large array for switching in an opticalnetwork. It is therefore desirable to provide an opto-mechanicalmicromachined micro-switch that avoids the heating problems associatedwith the continuous application of electric current.

SUMMARY OF THE INVENTION

[0007] To overcome the shortcomings of existing optical switchesdescribed above, the present invention relates to an opto-mechanicalmicro-switch assembly that is more efficient, more mechanically andoptically stable, and consumes less energy. Specifically, this inventionrelates to a novel magnetic latching mechanism for the mirror in themicro-switch. The present invention also relates to a method ofoperating the opto-mechanical micro-switch assembly.

[0008] According to one embodiment of the present invention, the overallassembly of a micromachined switch consists of an inner frame pivotallyconnected to an outer frame formed from a monocrystalline siliconsubstrate via torsion beams. The structure of the inner frame includes alight-reflecting (mirror) surface. A current can be applied to coilsthat are attached to the inner frame. Permanent magnets are attachedonto the outer frame. Because of the interaction of the current and themagnetic field of the permanent magnets, an electromagnetic force causesthe inner frame, and thereby the mirror, to pivot about the beams. Whenthe mirror rotates to a certain position, the mirror surface intercepts(blocks or reflects) light transmitted via fiber optic networks. It isoften required to maintain the mirror at such positions for a length oftime during the operation of the micro-switch. The present inventionprovides a novel mechanism for latching the mirror for such purpose.

[0009] According to one embodiment of the present invention, a piece ofmagnetic material (e.g., Permalloy) is attached to the lower portion ofthe moving/rotatable inner frame. The outer frame consists of layers ofa silicon substrate, a permanent magnet, and a nickel/iron base. Theselayers are etched onto each other using prevailing art ofmicromachining. Upon applying an initial electromagnetic force to rotatethe inner frame past a threshold, the Permalloy piece is brought closerto the permanent magnet layer. Due to the attraction between thePermalloy piece on the inner frame and the permanent magnet layer in theouter frame, the inner frame of the opto-mechanical micro-switch can belatched onto the outer frame without continuous application of electriccurrent to maintain the electromagnetic force to keep the inner frame inthe rotated position.

[0010] In another embodiment of the present invention, a Permalloy pieceis attached to the permanent magnet layer in the outer frame to focusthe magnetic field at the Permalloy piece on the inner frame. Duringpivotal movements, the Permalloy piece already attached to the innerframe will be drawn to the Permalloy piece on the outer frame. Theaddition of the Permalloy piece on the outer frame increases theeffective magnetic force, which attracts and holds the two Permalloypieces in a latched-on position.

[0011] The above, as well as additional objects, features, andadvantages of the present invention will become apparent in thefollowing detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a fuller understanding of the nature and advantages of thepresent invention, as well as the preferred mode of use, referenceshould be made to the following detailed description read in conjunctionwith the accompanying drawings. In the following drawings, likereference numerals designate like or similar parts throughout thedrawings.

[0013]FIG. 1 is a perspective view showing a micromachined micro-switchstructure in accordance with one embodiment of the invention.

[0014]FIG. 2 is a plan view of the opto-mechanical micro-switch of FIG.1 in relation to light source and detectors.

[0015]FIG. 3 is a sectional view of the opto-mechanical micro-switchtaken along line 3-3 in FIG. 2 at the “switch off” stage.

[0016]FIG. 4 is a plan bottom view of the inner frame in FIG. 3 showingone embodiment of the present invention with Permalloys.

[0017]FIG. 5 is a plan bottom view of the inner frame in FIG. 3 showinganother embodiment of the present invention with Permalloys.

[0018]FIG. 6 is a sectional view of the opto-mechanical micro-switch ofFIG. 3 rotating towards the latched position.

[0019]FIG. 7 is a graph showing the relationship of various statictorques for switching on an opto-mechanical micro-switch according toone embodiment of the present invention.

[0020]FIG. 8 is a sectional view of the opto-mechanical micro-switch ofFIG. 3 at the “switch-on” stage.

[0021]FIG. 9 is a graph showing the relationship of various statictorques for latching on an opto-mechanical micro-switch according to oneembodiment of the present invention.

[0022]FIG. 10 is a sectional view of the opto-mechanical micro-switch ofFIG. 3 at the “switch starts off” stage with latch on.

[0023]FIG. 11 is a graph showing the relationship of various statictorques for unlatching an opto-mechanical micro-switch according to oneembodiment of the present invention.

[0024]FIG. 12 is a graph showing the changes of coil actuation currentduring the operation of an opto-mechanical micro-switch according to oneembodiment of the present invention.

[0025]FIG. 13 is a sectional view of an opto-mechanical micro-switchwith the Permalloy on the stop die at the latched on position inaccordance with another embodiment of the present invention.

[0026]FIG. 14 is a sectional view of an opto-mechanical micro-switchwith the Permalloy on the stop die at the latched off position inaccordance with another embodiment of the present invention.

[0027]FIG. 15 is a perspective bottom view of the inner frame in FIG. 3showing one embodiment of the present invention with Permalloy.

[0028]FIG. 16 is a perspective bottom view of the inner frame in FIG. 3showing another embodiment of the present invention with Permalloys.

[0029]FIG. 17 is a perspective bottom view of the inner frame in FIG. 3,showing another embodiment of the present invention with Permalloys.

[0030]FIG. 18 is a graph showing the relationship between the criticaltorque and the current of the coil.

[0031]FIG. 19 is a cross-sectional view taken along line 19-19 in FIG. 5of the inner frame with the substrate of the outer frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] This invention is described in a preferred embodiment in thefollowing description with reference to the drawings. While thisinvention is described in terms of the best mode for achieving thisinvention's objectives, it will be appreciated by those skilled in theart that variations may be accomplished in view of these teachingswithout deviating from the spirit or scope of the invention. Thisdescription is made for the purpose of illustrating the generalprinciples of the invention and should not be taken in a limiting sense.The scope of the invention is best determined by reference to theappended claims.

[0033] An opto-mechanical micromachined switch is described in U.S.patent application Ser. No. 09/366,428 filed Aug. 2, 1999, assigned toIntegrated Micromachines, Inc., the assignee of the present invention.That application is fully incorporated by reference herein.

[0034] An opto-mechanical micro-switch, according to one embodiment ofthe present invention, comprises a micromachined structure that isformed from a monocrystalline silicon substrate. Referring now to FIG.1, there is shown a perspective view of the overall assembly of suchmicromachined structure 100, which is formed from a monocrystallinesilicon substrate 110 having an upper surface 112 that lies in the {100}plane of monocrystalline silicon substrate 110. The single crystalstructure of monocrystalline silicon substrate 110 is recommendedbecause it provides mechanical advantages, such as superior stiffness,durability, fatigue and deformation characteristics. In addition,monocrystalline silicon substrates are relatively inexpensive andreadily available. Further, batch fabrication techniques usingmonocrystalline silicon are well established. Monocrystalline siliconsubstrate 110 can be economically micromachined to form relativelydefect-free micromachined structure 100. In other embodiments, substrate110 may be formed using other materials.

[0035] Micromachined structure 100 includes an outer frame 120 and aninner frame 130. Inner frame 130 is pivotally connected to outer frame120 by beams 40. A controller 99 is configured to apply an externalforce to rotate the inner frame 130 about beams 40. Inner frame 130 hasoutward-facing flat surface 138. As described below, outward-facing flatsurface 138 is utilized as a light reflecting/blocking surface thateither reflects an incident light beam (i.e., when a light reflecting(mirror) material is deposited on the surface 138), or blocks theincident light beam (e.g., when the surface 138 is partially or fullyopaque).

[0036]FIG. 2 is a plan view showing an opto-mechanical micro-switch 300incorporating the micromachined structure 100 (shown in FIG. 1) and therelationship to light source and sensors in accordance with oneembodiment of the present invention. In FIG. 2 the opto-mechanicalmicro-switch 300 includes a light source 14, a first light receiver 15,a second light receiver 16, and micromachined structure 100, which islocated adjacent to light source 14 and light receivers 15 and 16. Asindicated above, micromachined structure 100 includes an outer frame 120and an inner frame 130 that is surrounded by and pivotally connected tothe outer frame 120. Inner frame 130 includes an outward-facing flatsurface 138 that is used to selectively reflect a light beam 18 fromlight source 14 to first light receiver 15. In the embodiment shown, theplanar size of the inner frame 130 is on the order of 2 mm×2 mm.

[0037] Although a single opto-mechanical micro-switch 300 is shown inFIG. 2, the methods and structure of the present invention may beutilized to produce a multi-switch device including an array of multiplemicromachined structures 100 formed on a single substrate. Becausemicromachined structure 100 is formed using a batch process, multipleinteracting micro-switches may be formed during the same fabricationprocess, thereby providing alignment of multiple mirror surfaces toproduce a multi-switch arrangement. In addition, to manufacture themicromachined structure 100 and the micro-switch 300, etch-stopdiffusion, silicon nitride deposition, Permalloy formation, anisotropicetching, frame separation, metallization can be performed using themanufacturing techniques disclosed in U.S. patent application Ser. No.09/366,428 filed Aug. 2, 1999, assigned to Integrated Micromachines,Inc., the assignee of the present invention.

[0038] One aspect of the present invention is shown in FIGS. 3-5. FIG. 3is a sectional view, taken along line 3-3 in FIGS. 2 and 4, ofopto-mechanical micro-switch incorporating an embodiment of the presentinvention. In FIG. 3, the micro-switch is in its “switch off” position.The {100} plane of monocrystalline silicon substrate 110 defines uppersurface 112. The {111} plane of monocrystalline silicon substrate 110defines the outward-facing flat surface 138 of the inner frame 130. Asis characteristic of a single silicon crystal, the {100} plane(indicated as horizontal plane P100) intersects the {111} plane(indicated as plane P111) at an angle α equal to 54.7°.

[0039] The monocrystalline silicon substrate is formed such that theupper and lower surfaces lie in {100} planes of the substrate. Theanisotropic etchant stops at the {111} plane of the monocrystallinesilicon substrate, thereby producing the flat wall at a known anglerelative to the upper and lower surfaces of the substrate. In the KOHetching process, a notch 23 is formed by etching along the {111} crystalplane of the silicon substrate layer 24 so that it can be aligned withthe etched {111} plane of the substrate 110 above it. The notch 23 is arecess that allows the layer of substrate 110 to align accurately ontothe layer of substrate 24. The angle of the KOH etched plane is about54.7° to the {100} plane of the substrate 24.

[0040] When the inner frame 130 is rotated a predetermined amountrelative to the outer frame 120, the outward-facing flat surface 138 isrotated into a raised position to selectively obstruct or reflect lightpassing from the light source 14 to the light receiver 15/16 of theopto-mechanical micro-switch 300. This is known as the “switch-on”position and is shown in FIG. 8.

[0041] In accordance with one embodiment of the present invention, themethod of operating the micro-switch is provided below. Actuation ofmicromachined structure 100 in the opto-mechanical micro-switch 300arrangement requires the application of a force (e.g., electromagnetic)to inner frame 130 that causes pivoting or rotation of inner frame 130relative to outer frame 120 around beam 40 (see FIGS. 4 and 5) about theaxis of rotation 42. Inner frame 130 is selectively pivoted into aposition in which the plane of the light reflecting/blocking, outwardfacing flat surface 138 is perpendicular to upper surface 112 as shownin FIG. 8. In this manner, the opto-mechanical micro-switch 300 operatesby pivoting from a first position shown in FIG. 3, in which end Y islocated at or below plane P100 defined by upper surface 112 (i.e., the“switch-off” position), to the upright (second) position shown in FIG.8, in which the plane P111 defining surface 138 intersects the planeP100 of substrate 110 at an angle of approximately 90° (i.e., the“switch-on” position). As indicated in FIG. 3, when inner frame 130 isin the “switch-off” position, light beam 18 is transmitted acrossmicromachined structure 100 from light source 14 to light receiver 16,thereby indicating a first switch state. However, as shown in FIG. 2,when the inner frame rotates upward, light beam 18 is reflected byoutward-facing flat surface 138 back to the light receiver 15 or blockedaltogether (not shown in figures), thereby indicating an alternateswitch state.

[0042] It is noted that the terms “switch-on” and “switch-off” arereferenced arbitrarily relative to two states of the switch. The “on”and “off” states of the switch may be interchanged between FIG. 3 andFIG. 8 without departing from the scope and spirit of the invention.

[0043] In one embodiment, a magnetic material such as a Ni—Fe materialcommercially available under the trademark Permalloy is provided on theinner frame 130, so that the inner frame can be latched onto the outerframe 120, without continuous application of electric current throughcoils attached to the inner frame 130. The electromagnetic force can beapplied through an external structure, mounted in close proximity tomicromachined structure 100 on a hybrid substrate, or integrated ontomicromachined structure 100.

[0044] As indicated in FIG. 3, a Permalloy piece 30 on the inner frameand a permanent magnet layer 26 in the outer frame are arranged tomaintain latching after pivoting/rotation. The Permalloy piece 30 isattached to the downward movable portion 32 at end X of inner frame 130.The magnet 26 lies between the silicon substrate layer 24 and thenickel/iron layer 28.

[0045]FIG. 19 shows the cross-sectional view of the inner frame 130along line 19-19 in FIG. 5 with reference to the outer frame. As seen inthese two figures, the inner frame 130 has permalloys 30b and 30c thatdo not contact the substrate 24. The width of the substrate 24 in FIG.19 does not extend to contact the permalloys 30b and 30c that aresuspended in the air without supports below them. The substrate 24 hasminimal contact area with the inner frame 130 to reduce stiction. Thisconfiguration can also be applied to the Permalloy configuration shownin FIG. 14.

[0046] As indicated above, FIG. 3 shows the initial position, or thefirst switch state or the “switch off” state. At this “switch-off”state, end Y remains at or below plane P100 with upward movable portion34 resting upon silicon substrate 24 at upper silicon surface 54. Thecoils 20, which lie on upper surface 112 of inner frame 130, arefabricated in accordance with techniques known to those skilled in theart. Coils 20 include a plurality of electrically conductive windings,which are electrically isolated from adjacent windings by an insulatingmaterial. As current flows through coils 20, an electromagnetic force isgenerated.

[0047] As the inner frame 130 begins to pivot from the “switch-off”state in FIG. 3 to the “switch-on” state as shown in FIG. 8, the innerframe 130 begins to pivot in an anti-clockwise direction under theinteraction of the current and the magnetic field caused by thepermanent magnet layer in the outer frame. As the inner frame begins topivot (see FIG. 6), a reactive torque, τ_(beam), is generated from thetorsion of the beams 40 and it gradually increases. On the other hand,the torque generated by the electromagnetic force caused by a constantcurrent in the coils, τ_(coil), generally decreases with rotation of theinner frame 130 in the anti-clockwise direction (the τ_(coil) is notconstant because of the change in relative position between the coils 20and the permanent magnet 26 and the change in the direction of thecomponent of the magnetic force attributing to torque on the innerframe). At the same time, the torque caused by the attractive forcebetween the Permalloy piece 30 and the magnet 26, τ_(permalloy),continues to increase. In order for the inner frame 130 to be able torotate, the following relationship must be met:|τ_(permalloy)+τ_(coil)|>|τ_(beam)|.

[0048] When the angle of inclination (or rotation) of the inner framereaches a critical angle (θ_(critical)), which is measured about theaxis of rotation 42, τ_(permalloy) is sufficient to counteract beam evenin the absence of the current induced τ_(coil). Beyond θ_(critical), aslong as τ_(permalloy)>τ_(beam), the inner frame will continue to rotateto an upper silicon surface 54 as shown in FIG. 8, and remain in thisposition (i.e., latched on) in the absence of any coil current. Themagnetic force from the permanent magnet layer 26 holds the Permalloypiece 30 down, against the bias of τ_(beam), thus maintaining the innerframe 130 in the latched position. τ_(latching) is the value ofτ_(permalloy) at the latched position. FIG. 7 shows that afterθ_(critical), τ_(permalloy) is greater than τ_(beam), thus ensuring theswitching on state. FIG. 18 further shows that the current I_(coil)required to ensure rotation of the inner frame lies within a range ofpossibilities. One can control the applied coil current to provide achanging τ_(coil) that just exceeds τ_(beam)-τ_(permalloy) (or Δτ) alongthe rotation of the inner frame from θ=0 to θ=θ_(critical). Thisrequires more complex control, but would minimize the applied current.θ_(critical) is the greatest value of τ_(beam)-τ_(permalloy) duringrotation to θ_(critical). As long as the entire I_(coil) curve lies onor above the Δτ curve, any of the I_(coil) curves will allow thenecessary current for the desired rotation of the inner frame forlatching. As shown in FIG. 12, in yet another embodiment of the presentinvention, once the threshold θ_(critical) is passed, a reverse currentof an appropriate amount may be applied through the coils in order togenerate a torque (<|τ_(permalloy)-τ_(beam)|) in a clockwise directionto counter the τ_(permalloy) that is in excess of τ_(beam) and a torqueattributed to the rotational momentum of the inner frame. The purpose ofthis reverse torque is to soften the impact when the Permalloy pieceattached to the inner frame hits the outer frame.

[0049] As indicated in FIGS. 8 and 9, in one embodiment of the presentinvention, when the angle of inclination, θ, reaches 35.24°, the innerframe 130 is latched onto the outer frame 120 at silicon substrate 24.The value, 35.24°, is the difference of 90° and 54.76°, which is theangle of intersection of P111 of the inner frame and the upper surface112 of the outer frame 120 when the inner frame is in its “switch off”position. At this angle of inclination, the flat surface of P111 of theinner frame 130 will form a 90° angle with the upper surface 112 of theouter frame 120. As mentioned before, even though the power is released,the magnetic force between the magnet 26 and Permalloy piece 30maintains the latching position. As shown in FIG. 8, in this latched onposition, all light from the light source 14 is reflected to receiver 15(see FIG. 2; receiver 15 is obscured from view by light source 14 inFIG. 8) or blocked from receiver 16.

[0050]FIGS. 10 and 11 demonstrate the process in which the latched-onswitch returns to its “off” position. When the switch is to beunlatched, power is applied so that a reverse current runs through thecoils 20. As shown in FIG. 8, the latching torque in the anti-clockwisedirection is the torque generated by the magnetic force between thePermalloy piece and the permanent magnet, i.e., τ_(latching). To unlatchthe inner frame, two opposing torques to the latching torque come intoplay, the torque of the beam, τ_(beam), and the torque generated by theinteraction of the reverse current through the coils 20 and the magneticfield from the permanent magnet 26, τ_(coil). As shown in FIG. 11, atthe point of unlatching, |τ_(unlatching)|=|τ_(coil)+τ_(beam)| must begreater than |τ_(permalloy)| to initiate rotation of the inner framefrom its latched position. τ_(coil) must be maintained such that it isgreater than |τ_(permalloy)-τ_(beam)| at all times to maintain rotationof the inner frame, until the inner frame reaches θ_(critical). If aconstant reverse current is applied, τ_(coil) should be the maximumvalue of |τ_(permalloy)-τ_(beam)| (i.e., at the latched positionτ_(latching)-τ_(beam) in FIG. 11) to ensure sufficient τ_(coil). If avariable current is applied, τ_(coil) may be decreased as the innerframe rotates from the latch position. (It is noted that θ_(critical)for clockwise rotation (unlatching) may be slightly different fromθ_(critical) for anti-clockwise rotation (latching) because ofrotational momentum of the inner frame, a dynamic component that causeshysteresis in θ_(critical) and other parameters between rotations in thetwo directions. The reverse current may be released once the criticalangle, θ_(critical), is passed. As indicated before and as shown in FIG.11, after this point, τ_(beam) is greater than τ_(permalloy), and thusthe inner frame will continue to tilt in the anti-clockwise directionuntil its end Y rests on the silicon substrate 24. In yet anotherembodiment of the present invention, once the critical point is passed,a current of an appropriate amount is applied through the coils togenerate a torque (less than |τ_(beam)-τ_(permalloy)|) in theanti-clockwise direction to counter the excessive torque of the beamsand the rotational momentum of the inner frame. The purpose is to softenthe impact of end Y of the inner frame when it returns to its original“off” position and rests on the silicon substrate 24 in the outer frame.

[0051]FIG. 12 further illustrates the behavior (current as a function oftime) of the opto-mechanical micro-switch 300 from the “switch off” to“switch on” and then back to “switch off” states under control of thecontroller 99, according to one embodiment of the present invention. Attime 0, the micro-switch is at the “switch off” state as illustrated inFIG. 3. A current, I_(critical), is applied through the coils attachedto the inner frame between t=0 and ti to rotate the inner frame from θ=0to θ_(critical). The value of I_(critical) is chosen so that the innerframe will pivot through the critical angle of inclination,θ_(critical), beyond which, as indicated above, the torque generated bythe magnetic force between the Permalloy piece and the permanent magnetwill overcome the reactive torque of the beam, thus allowing latching tooccur with the current removed. Beyond t₁ and θ_(critical), a reversecurrent is applied through the coils to reduce the impact of thePermalloy piece onto the outer frame due to the excessive torque causedby the magnetic attraction between the Permalloy piece and the permanentmagnet over the reactive torque of the beam. At time t₂, the inner framereaches its “latched-on” position. At this point, no current needs to beapplied through the coils. The excessive magnetic torque, τ_(permalloy),over the beam torque, τ_(beam), will keep the inner frame in place. Whenunlatching, a reverse current is applied, so that the sum of theunlatching torque and the beam torque must be higher than the latchingmagnetic torque, thereby causing the inner frame to tilt back to itsoriginal starting position. The time t₄ is a time where the inner framehas tilted back, slightly beyond the critical angle. Since after t₄, thetorque of the beam is higher than the magnetic torque, the inner framewill continue to tilt toward its starting position, even without anycontinuous current. However, again in order to reduce the impact whenthe inner frame hits the upper surface 54 of the silicon substrate ofthe outer frame, a positive current is applied to counter the excessivetorque of the beam over the magnetic torque. Impact reducing isnecessary during latching to prevent the end X of the inner frame 130from making contact with the outer frame 120 that may cause structuraldamage; impact reducing is also necessary during “switching off” toprevent the end Y of the inner frame 130 from hitting the upper siliconsurface 54 with excess force.

[0052]FIG. 13 shows yet another embodiment of the present invention. Anadditional Permalloy piece 60 is added to the permanent magnet 26 tofocus the magnetic field against the Permalloy piece 30. In FIG. 13, thePermalloy piece 60 is incorporated within the silicon substrate 24 andplaced directly on top of, or in close proximity to, the permanentmagnet layer 26 to allow magnetization of the Permalloy piece 60. Thisarrangement increases the magnetic force on the Permalloy piece 30 byfocusing the magnetic flux of layer 26 on the Permalloy piece 30, whichattracts the Permalloy piece 30 towards lower stationary portion 64 andholds it in the latched on position.

[0053]FIG. 14 shows yet another embodiment of the present invention. Asshown in FIG. 14, a Permalloy piece 62 is added to the silicon substratelayer 24. Further, the Permalloy piece 62 is placed directly on top of,or in close proximity to, the permanent magnet layer 26, in order toallow magnetization of the Permalloy piece 62. An additional Permalloypiece 30b/30c/30d is added to the lower portion of end Y of the innerframe 130. The magnetized Permalloy piece 62 keeps the end Y of innerframe 130 attached to the upper stationary portion 66. This embodimentserves to securely hold the inner frame 130 in place in the non-biasedstate (switch-off) against external perturbations, and to reduce theforce required to unlatch from the switch-on state.

[0054]FIGS. 4 and 5 show two plan bottom views of inner frame 130 withdifferent Permalloy deposit embodiments. FIG. 4 shows Permalloy 30a witha stop edge 44, which allows for silicon-to-silicon contact when theswitch is on and the inner frame is latched onto the outer frame. Thestop edge 44 avoids the Permalloy-to-silicon contact. Thesilicon-to-silicon contact prevents the constant impact of the Permalloypiece during the operations of the micro-switch. Not only does itprevent damage deformation but it also avoids stiction; a tremendousforce is required for separation once there is contact. FIG. 15, aperspective bottom view of FIG. 4, shows one embodiment of the presentinvention with the Permalloy 30a on one side of the inner frame 130.Another embodiment of the present invention in FIG. 5 shows Permalloy30a and stop edge 44 with the addition of Permalloys 30b and 30c at thelower corners of the inner frame 130. FIG. 16, a perspective bottom viewof FIG. 5, also shows stop edge 45 in between Permalloy 30b and 30c. Inyet another embodiment of the present invention, FIG. 17 shows anadditional Permalloy 30d with stop edges 45a and 45b. These additionalPermalloys allow for increased latching strength in another embodimentas shown in FIG. 14.

[0055] To manufacture a micromachined structure, reference is made toU.S. patent application Ser. No. 09/366,428 filed Aug. 2, 1999, assignedto Integrated Micromachines, Inc., the assignee of the presentinvention, which is fully incorporated by reference herein. Such patentapplication discloses a process that provides one skilled in the artwith the steps to manufacture the following: an outer frame and an innerframe, pivotally coupled to the outer frame, which is rotatable about anaxis of rotation from a first position to a second position relative tothe outer frame when an external force is applied, and wherein the innerframe is biased to return to the first position in the absence of theexternal force, and providing a permanent magnet on the outer frame. Inthe present invention, the method of manufacturing a micromachinedstructure further includes the step of forming the Permalloy, or amagnetic material, on the inner frame.

[0056] While the present invention has been particularly shown anddescribed with reference to the preferred embodiments, it will beunderstood by those skilled in the art that various changes in form anddetail may be made without departing from the spirit, scope, andteaching of the invention. Accordingly, the disclosed invention is to beconsidered merely as illustrative and limited in scope only as specifiedin the appended claims.

We claim:
 1. A micromachined structure comprising: an outer frame; aninner frame pivotally coupled to the outer frame, wherein the innerframe is rotatable about an axis of rotation from a first position to asecond position relative to the outer frame when an external force isapplied, and wherein the inner frame is biased to return to the firstposition in the absence of the external force; and latching means formaintaining the inner frame in the second position in the absence of theexternal force.
 2. A micromachined structure according to claim 1,wherein said inner frame has a reflective surface provided thereon.
 3. Amicromachined structure according to claim 1, wherein said externalforce is an electromagnetic force.
 4. A micromachined structureaccording to claim 1, wherein said latching means comprises means forcreating a magnetic attraction between the inner frame and the outerframe.
 5. A micromachined structure according to claim 4, wherein saidlatching means comprises: a permanent magnet on the outer frame; and amagnetic material on the inner frame.
 6. A micromachined structureaccording to claim 5, wherein said magnetic material is Permalloy.
 7. Amicromachined structure according to claim 5, wherein the inner framehas first and second sides relative to the axis of rotation, and theouter frame has a stop against which the inner frame rests in the secondposition, and said magnetic material is positioned on the first side ofthe inner frame that is closer to the stop when the inner frame isbiased to the second position.
 8. A micromachined structure according toclaim 7, wherein said magnetic material is positioned such that when theinner frame rotates to the second position and rests against the stop,the stop does not contact the magnetic material.
 9. A micromachinedstructure according to claim 7, further comprising additional magneticmaterials positioned on the second side of the inner frame to focusmagnetic flux of the permanent magnet against the magnetic material. 10.A micromachined structure according to claim 9, wherein said magneticmaterial is positioned such that when the inner frame rotates to thefirst position and rests against the stop, the stop does not contact themagnetic material.
 11. A micromachined structure according to claim 5,wherein said latching means further comprises: a magnetic material onthe outer frame that is positioned closer to the first side of the innerframe to focus the magnetic flux of the permanent magnet against themagnetic material on the first side of the inner frame.
 12. Amicromachined structure according to claim 5, wherein said latchingmeans further comprises: a magnetic material on the outer frame that ispositioned closer to the second side of the inner frame to focus themagnetic flux of the permanent magnet against the magnetic material onthe second side of the inner frame.
 13. A method of rotating an innerframe with respect to an outer frame, comprising the steps of: applyingan external force to rotate the inner frame from a first to a secondposition; removing the external force; and applying a magneticattraction between the inner frame and the outer frame in the absence ofthe external force.
 14. A method as in claim 13 wherein the magneticattraction is applied prior to removing the external force.
 15. A methodas in claim 13 wherein the step of applying a magnetic attractioncomprises the steps of: providing a permanent magnet on the outer frame;and providing a magnetic material on the inner frame, wherein themagnetic material is positioned in relation to the permanent magnet toallow magnetic attraction between the permanent magnet and the magneticmaterial.
 16. A method as in claim 13, further comprising the step of:applying a force to reduce momentum of the inner frame before the innerframe reaches the second position.
 17. A method as in claim 16, furthercomprising the step of: applying an external force in excess of themagnetic attraction at the second position to return the inner frame tothe first position.
 18. A method as in claim 16, further comprising thestep of: applying a force to reduce momentum of the inner frame beforethe inner frame reaches the first position.
 19. A method ofmanufacturing a micromachined structure, comprising the steps of:providing an outer frame; providing an inner frame pivotally coupled tothe outer frame, wherein the inner frame is rotatable about an axis ofrotation from a first position to a second position relative to theouter frame when an external force is applied, and wherein the innerframe is biased to return to the first position in the absence of theexternal force; providing a permanent magnet on the outer frame; andproviding a magnetic material on the inner frame.
 20. A micromachinedsystem, comprising: a micromachined structure that comprises an outerframe, an inner frame pivotally coupled to the outer frame, wherein theinner frame is rotatable about an axis of rotation from a first positionto a second position relative to the outer frame when an external forceis applied, and wherein the inner frame is biased to return to the firstposition in the absence of the external force, a latching means formaintaining the inner frame in the second position in the absence of theexternal force; and a controller configured to apply the external forceto rotate the inner frame to the second position and another externalforce to rotate the inner frame to the first position.
 21. An opticalswitch comprising: a micromachined structure that comprises an outerframe; an inner frame pivotally coupled to the outer frame, wherein theinner frame has a reflective surface, and is rotatable about an axis ofrotation from a first position where the reflective surface is facing afirst direction in to a second position relative to the outer framewhere the reflective surface is facing another direction when anexternal force is applied, and wherein the inner frame is biased toreturn to the first position in the absence of the external force; and alatching means for maintaining the inner frame in the second position inthe absence of the external force.
 22. An optical network comprising: atleast one radiation source; and at least one detector; and at least oneoptical switch selectively directing radiation from the radiation sourceto the detector, said optical switch comprising: a micromachinedstructure that comprises an outer frame; an inner frame pivotallycoupled to the outer frame, wherein the inner frame has a reflectivesurface, and is rotatable about an axis of rotation from a firstposition where the reflective surface is facing a first direction in toa second position relative to the outer frame where the reflectivesurface is facing another direction when an external force is applied,and wherein the inner frame is biased to return to the first position inthe absence of the external force; and a latching means for maintainingthe inner frame in the second position in the absence of the externalforce.
 23. A micromachined structure comprising: a first member having afirst surface etched along a crystal plane; and a second member having anotch having a second surface etched along a similar crystal plane,wherein the first member and the second member are aligned with eachother by positioning the first surface against the second surface. 24.The micromachined structure according to claim 23, wherein the firstmember and the second member are made of silicon.
 25. The micromachinedstructure according to claim 24, wherein the first surface and thesecond surface are etched along a crystal plane at an angle of 54.7degrees.
 26. The micromachined structure according to claim 24, whereinthe first surface and the second surface are etched along the {111}crystal plane.
 27. The micromachined structure according to claim 23,wherein the first member has a bottom surface and the second member hasa top surface, whereby the first member is layered on the second memberso that the bottom surface and the top surface make substantial contactwith each other.